Peroneal tendon injuries: tendinitis, tears and subluxation

What are the peroneal tendons?

Two tendons, the peroneus longus and the peroneus brevis, run down the outer side of the lower leg. They pass behind the bony bump of the outer ankle (the fibula) and along the outer edge of the foot. They turn the foot outward and help keep the ankle stable, which helps prevent sprains.^[1,4,2] The brevis attaches to the base of the fifth metatarsal, the long bone behind the little toe. The longus crosses under the foot to the inner side. Behind the ankle bone, the two tendons share a sheath. They run through a groove, and a band of tissue called the retinaculum holds them in it.^[3]

Problems with these tendons fall into three groups. The first is inflammation of the tendons and their sheath (tendinitis or tenosynovitis). The second is a tendon that slips out of its groove (subluxation or dislocation). The third is a split or tear within the tendon.^[2]

Symptoms

The symptoms depend on the type of injury:

• Tendinitis: pain, swelling and warmth along the outer ankle
• A sudden (acute) tear: sharp pain and swelling, with weakness or a feeling that the ankle is unstable
• A gradual (degenerative) tear: occasional outer ankle pain that comes and goes over years, sometimes with a change in the arch
• Subluxation: a snapping sensation behind the outer ankle bone, pain, and instability^[1]

What causes peroneal tendon injuries?

Injuries come from repeated ankle motion in sports such as running, from trauma such as an ankle sprain, or from overuse. People with high arches have a higher risk.^[1] Peroneal problems often go along with other conditions of the foot and ankle. These include ankle instability and a hindfoot that is tilted inward or outward. Differences in anatomy, such as a low-lying muscle belly or an extra muscle (the peroneus quartus), are linked to tears and subluxation.^[2,3] A high-arched foot that turns inward puts extra load on the outer border of the foot and can contribute to ankle instability, peroneal tendinitis and stress fractures.^[6] See cavus foot and chronic ankle instability.

How peroneal tendon injuries are evaluated

The examination looks at your foot type (a high arch or a flat foot). It presses on the tendons in the groove behind the outer ankle bone while you turn the foot outward against resistance. It also tests the ligaments of the outer ankle, which can be injured at the same time.^[2] Imaging helps confirm the diagnosis: X-rays, ultrasound and MRI can each contribute.^[2,1] X-ray and ultrasound are available on site at our practice; see foot and ankle imaging.

Peroneal injuries can be mistaken for a lateral ankle ligament injury, and both can be present, so a careful evaluation matters.^[2,4] See also ankle pain and swelling.

Non-surgical care

Treatment usually starts without surgery. Options include immobilization in a cast, splint or boot, anti-inflammatory medicine, physical therapy, and bracing during activity.^[1] People who are less physically demanding on their ankles generally do well with a non-surgical approach.^[4]

When a tendon has slipped out of place, the choice between a cast and surgery is debated. A systematic review of small studies found that the tendon slipped out again in about 60% of people treated with taping or strapping. The rate was about a third after a cast worn for at least four weeks, and one in six after a non-weight-bearing cast worn for six weeks or more. The authors concluded that a non-weight-bearing cast could be a reasonable alternative to surgery, based on limited data.^[7]

When surgery is considered

Surgery is considered when non-surgical treatment doesn’t control symptoms, for a torn tendon that causes ongoing pain, or for a tendon that keeps slipping. High-demand patients, such as athletes, may benefit more from early surgery.^[1,4]

The operation depends on what is found. It can involve cleaning up the tendon and its sheath, repairing a tear, or tightening or rebuilding the band that holds the tendons in place. It can also involve deepening the groove. When the tendon is too damaged to repair, a nearby tendon can be moved or a graft used.^[5,8] A systematic review of nine studies and 336 ankles treated for peroneal tendon tears found that pain and function scores improved substantially after surgery. About four in ten patients had some complication, most often minor ankle pain.^[5] Surgery for a tendon that keeps slipping also improved function in a review of 31 studies, though the quality of the studies varied.^[8] Recommendations rest mostly on case series and expert opinion rather than large trials.^[2]

For the operations, recovery and risks, see peroneal tendon surgery. When ligament looseness is part of the problem, see ankle ligament repair and reconstruction.

When to seek care

Consider an evaluation if outer ankle pain lasts more than a few weeks after a sprain. The same goes for a snap behind the ankle bone, an ankle that keeps giving way, or pain that returns whenever you go back to sport.